This paper, based on cross-regional empirical research, provides an integrated analytical framework for understanding the emergence of populism in seemingly different political contexts in both Europe (including Greece, France and the Netherlands) and Latin America (including Peru and Venezuela). It is found that, given an appropriate context, political leadership is the most important factor for setting in motion a number of interdependent causal mechanisms that may produce populism. Those mechanisms include the politicization of social resentment, the formation of new cleavage lines, and intense polarization. When successfully emergent, populism’s first and foremost outcome is the creation of new parties, or movements, of a distinctly personalist appeal. The causal explanation proposed in this paper is both parsimonious and credible. It also points to specific research themes related to successfully emergent populism.